An Update on Quantum Cryptography

Although written aboutfifteen years ago, Wiesner’s seminal paper, to which the origin of quantum cryptography must be traced back, did not appear in print until the spring of 1983 [W83]. The first published account of these ideas thus appeard in the proceedings of the second annual CRYPTO conference [BBBW83]. However, the concepts presented there were mostly of theoretical interest, because the technology involved in implementing them wouldhave been far beyond the reach of our current knowledge. In particular, single polarized photons had to be trapped, bounding back and forth between perfectly reflecting mirrors, and perfect efficiency in photon detection was required. To make up for this inconvenience, we could prove that no technology whatsoever, as well as no amount of computing power, could break some of our schemes, as long as some of the most fundamental principles of quantum physics hold true.